Re: [PATCH 00/27] ext4: use iomap for regular file's buffered I/O path and enable large folio

Sedat Dilek
2024-10-23T12:14:08Z

On Tue, Oct 22, 2024 at 11:22 AM Zhang Yi <yi.zhang@huaweicloud.com> wrote:
>
> On 2024/10/22 14:59, Sedat Dilek wrote:
> > On Tue, Oct 22, 2024 at 5:13 AM Zhang Yi <yi.zhang@huaweicloud.com> wrote:
> >>
> >> From: Zhang Yi <yi.zhang@huawei.com>
> >>
> >> Hello！
> >>
> >> This patch series is the latest version based on my previous RFC
> >> series[1], which converts the buffered I/O path of ext4 regular files to
> >> iomap and enables large folios. After several months of work, almost all
> >> preparatory changes have been upstreamed, thanks a lot for the review
> >> and comments from Jan, Dave, Christoph, Darrick and Ritesh. Now it is
> >> time for the main implementation of this conversion.
> >>
> >> This series is the main part of iomap buffered iomap conversion, it's
> >> based on 6.12-rc4, and the code context is also depend on my anohter
> >> cleanup series[1] (I've put that in this seris so we can merge it
> >> directly), fixed all minor bugs found in my previous RFC v4 series.
> >> Additionally, I've update change logs in each patch and also includes
> >> some code modifications as Dave's suggestions. This series implements
> >> the core iomap APIs on ext4 and introduces a mount option called
> >> "buffered_iomap" to enable the iomap buffered I/O path. We have already
> >> supported the default features, default mount options and bigalloc
> >> feature. However, we do not yet support online defragmentation, inline
> >> data, fs_verify, fs_crypt, ext3, and data=journal mode, ext4 will fall
> >> to buffered_head I/O path automatically if you use those features and
> >> options. Some of these features should be supported gradually in the
> >> near future.
> >>
> >> Most of the implementations resemble the original buffered_head path;
> >> however, there are four key differences.
> >>
> >> 1. The first aspect is the block allocation in the writeback path. The
> >> iomap frame will invoke ->map_blocks() at least once for each dirty
> >> folio. To ensure optimal writeback performance, we aim to allocate a
> >> range of delalloc blocks that is as long as possible within the
> >> writeback length for each invocation. In certain situations, we may
> >> allocate a range of blocks that exceeds the amount we will actually
> >> write back. Therefore,
> >> 1) we cannot allocate a written extent for those blocks because it may
> >> expose stale data in such short write cases. Instead, we should
> >> allocate an unwritten extent, which means we must always enable the
> >> dioread_nolock option. This change could also bring many other
> >> benefits.
> >> 2) We should postpone updating the 'i_disksize' until the end of the I/O
> >> process, based on the actual written length. This approach can also
> >> prevent the exposure of zero data, which may occur if there is a
> >> power failure during an append write.
> >> 3) We do not need to pre-split extents during write-back, we can
> >> postpone this task until the end I/O process while converting
> >> unwritten extents.
> >>
> >> 2. The second reason is that since we always allocate unwritten space
> >> for new blocks, there is no risk of exposing stale data. As a result,
> >> we do not need to order the data, which allows us to disable the
> >> data=ordered mode. Consequently, we also do not require the reserved
> >> handle when converting the unwritten extent in the final I/O worker,
> >> we can directly start with the normal handle.
> >>
> >> Series details:
> >>
> >> Patch 1-10 is just another series of mine that refactors the fallocate
> >> functions[1]. This series relies on the code context of that but has no
> >> logical dependencies. I put this here just for easy access and merge.
> >>
> >> Patch 11-21 implement the iomap buffered read/write path, dirty folio
> >> write back path and mmap path for ext4 regular file.
> >>
> >> Patch 22-23 disable the unsupported online-defragmentation function and
> >> disable the changing of the inode journal flag to data=journal mode.
> >> Please look at the following patch for details.
> >>
> >> Patch 24-27 introduce "buffered_iomap" mount option (is not enabled by
> >> default now) to partially enable the iomap buffered I/O path and also
> >> enable large folio.
> >>
> >>
> >> About performance:
> >>
> >> Fio tests with psync on my machine with Intel Xeon Gold 6240 CPU with
> >> 400GB system ram, 200GB ramdisk and 4TB nvme ssd disk.
> >>
> >> fio -directory=/mnt -direct=0 -iodepth=$iodepth -fsync=$sync -rw=$rw \
> >> -numjobs=${numjobs} -bs=${bs} -ioengine=psync -size=$size \
> >> -runtime=60 -norandommap=0 -fallocate=none -overwrite=$overwrite \
> >> -group_reportin -name=$name --output=/tmp/test_log
> >>
> >
> > Hi Zhang Yi,
> >
> > can you clarify about the FIO values for the diverse parameters?
> >
>
> Hi Sedat,
>
> Sure, the test I present here is a simple single-thread and single-I/O
> depth case with psync ioengine. Most of the FIO parameters are shown
> in the tables below.
>

Hi Zhang Yi,

Thanks for your reply.

Can you share a FIO config file with all (relevant) settings?
Maybe it is in the below link?

Link: https://packages.debian.org/sid/all/fio-examples/filelist

> For the rest, the 'iodepth' and 'numjobs' are always set to 1 and the
> 'size' is 40GB. During the write cache test, I also disable the write
> back process through:
>
> echo 0 > /proc/sys/vm/dirty_writeback_centisecs
> echo 100 > /proc/sys/vm/dirty_background_ratio
> echo 100 > /proc/sys/vm/dirty_ratio
>

^^ Ist this info in one of the patches? If not - can you add this info
to the next version's cover-letter?

The patchset and improvements are valid only for powerful servers or
has a notebook user any benefits of this?
If you have benchmark data, please share this.

I can NOT promise if I will give that patchset a try.

Best thanks.

Best regards,
-Sedat-

> Thanks,
> Yi.
>
> >
> >> == buffer read ==
> >>
> >> buffer_head iomap + large folio
> >> type bs IOPS BW(MiB/s) IOPS BW(MiB/s)
> >> -------------------------------------------------------
> >> hole 4K 576k 2253 762k 2975 +32%
> >> hole 64K 48.7k 3043 77.8k 4860 +60%
> >> hole 1M 2960 2960 4942 4942 +67%
> >> ramdisk 4K 443k 1732 530k 2069 +19%
> >> ramdisk 64K 34.5k 2156 45.6k 2850 +32%
> >> ramdisk 1M 2093 2093 2841 2841 +36%
> >> nvme 4K 339k 1323 364k 1425 +8%
> >> nvme 64K 23.6k 1471 25.2k 1574 +7%
> >> nvme 1M 2012 2012 2153 2153 +7%
> >>
> >>
> >> == buffer write ==
> >>
> >> buffer_head iomap + large folio
> >> type Overwrite Sync Writeback bs IOPS BW IOPS BW(MiB/s)
> >> ----------------------------------------------------------------------
> >> cache N N N 4K 417k 1631 440k 1719 +5%
> >> cache N N N 64K 33.4k 2088 81.5k 5092 +144%
> >> cache N N N 1M 2143 2143 5716 5716 +167%
> >> cache Y N N 4K 449k 1755 469k 1834 +5%
> >> cache Y N N 64K 36.6k 2290 82.3k 5142 +125%
> >> cache Y N N 1M 2352 2352 5577 5577 +137%
> >> ramdisk N N Y 4K 365k 1424 354k 1384 -3%
> >> ramdisk N N Y 64K 31.2k 1950 74.2k 4640 +138%
> >> ramdisk N N Y 1M 1968 1968 5201 5201 +164%
> >> ramdisk N Y N 4K 9984 39 12.9k 51 +29%
> >> ramdisk N Y N 64K 5936 371 8960 560 +51%
> >> ramdisk N Y N 1M 1050 1050 1835 1835 +75%
> >> ramdisk Y N Y 4K 411k 1609 443k 1731 +8%
> >> ramdisk Y N Y 64K 34.1k 2134 77.5k 4844 +127%
> >> ramdisk Y N Y 1M 2248 2248 5372 5372 +139%
> >> ramdisk Y Y N 4K 182k 711 186k 730 +3%
> >> ramdisk Y Y N 64K 18.7k 1170 34.7k 2171 +86%
> >> ramdisk Y Y N 1M 1229 1229 2269 2269 +85%
> >> nvme N N Y 4K 373k 1458 387k 1512 +4%
> >> nvme N N Y 64K 29.2k 1827 70.9k 4431 +143%
> >> nvme N N Y 1M 1835 1835 4919 4919 +168%
> >> nvme N Y N 4K 11.7k 46 11.7k 46 0%
> >> nvme N Y N 64K 6453 403 8661 541 +34%
> >> nvme N Y N 1M 649 649 1351 1351 +108%
> >> nvme Y N Y 4K 372k 1456 433k 1693 +16%
> >> nvme Y N Y 64K 33.0k 2064 74.7k 4669 +126%
> >> nvme Y N Y 1M 2131 2131 5273 5273 +147%
> >> nvme Y Y N 4K 56.7k 222 56.4k 220 -1%
> >> nvme Y Y N 64K 13.4k 840 19.4k 1214 +45%
> >> nvme Y Y N 1M 714 714 1504 1504 +111%
> >>
> >> Thanks,
> >> Yi.
> >>
> >> Major changes since RFC v4:
> >> - Disable unsupported online defragmentation, do not fall back to
> >> buffer_head path.
> >> - Wite and wait data back while doing partial block truncate down to
> >> fix a stale data problem.
> >> - Disable the online changing of the inode journal flag to data=journal
> >> mode.
> >> - Since iomap can zero out dirty pages with unwritten extent, do not
> >> write data before zeroing out in ext4_zero_range(), and also do not
> >> zero partial blocks under a started journal handle.
> >>
> >> [1] https://lore.kernel.org/linux-ext4/20241010133333.146793-1-yi.zhang@huawei.com/
> >>
> >> ---
> >> RFC v4: https://lore.kernel.org/linux-ext4/20240410142948.2817554-1-yi.zhang@huaweicloud.com/
> >> RFC v3: https://lore.kernel.org/linux-ext4/20240127015825.1608160-1-yi.zhang@huaweicloud.com/
> >> RFC v2: https://lore.kernel.org/linux-ext4/20240102123918.799062-1-yi.zhang@huaweicloud.com/
> >> RFC v1: https://lore.kernel.org/linux-ext4/20231123125121.4064694-1-yi.zhang@huaweicloud.com/
> >>
> >>
> >> Zhang Yi (27):
> >> ext4: remove writable userspace mappings before truncating page cache
> >> ext4: don't explicit update times in ext4_fallocate()
> >> ext4: don't write back data before punch hole in nojournal mode
> >> ext4: refactor ext4_punch_hole()
> >> ext4: refactor ext4_zero_range()
> >> ext4: refactor ext4_collapse_range()
> >> ext4: refactor ext4_insert_range()
> >> ext4: factor out ext4_do_fallocate()
> >> ext4: move out inode_lock into ext4_fallocate()
> >> ext4: move out common parts into ext4_fallocate()
> >> ext4: use reserved metadata blocks when splitting extent on endio
> >> ext4: introduce seq counter for the extent status entry
> >> ext4: add a new iomap aops for regular file's buffered IO path
> >> ext4: implement buffered read iomap path
> >> ext4: implement buffered write iomap path
> >> ext4: don't order data for inode with EXT4_STATE_BUFFERED_IOMAP
> >> ext4: implement writeback iomap path
> >> ext4: implement mmap iomap path
> >> ext4: do not always order data when partial zeroing out a block
> >> ext4: do not start handle if unnecessary while partial zeroing out a
> >> block
> >> ext4: implement zero_range iomap path
> >> ext4: disable online defrag when inode using iomap buffered I/O path
> >> ext4: disable inode journal mode when using iomap buffered I/O path
> >> ext4: partially enable iomap for the buffered I/O path of regular
> >> files
> >> ext4: enable large folio for regular file with iomap buffered I/O path
> >> ext4: change mount options code style
> >> ext4: introduce a mount option for iomap buffered I/O path
> >>
> >> fs/ext4/ext4.h | 17 +-
> >> fs/ext4/ext4_jbd2.c | 3 +-
> >> fs/ext4/ext4_jbd2.h | 8 +
> >> fs/ext4/extents.c | 568 +++++++++++----------------
> >> fs/ext4/extents_status.c | 13 +-
> >> fs/ext4/file.c | 19 +-
> >> fs/ext4/ialloc.c | 5 +
> >> fs/ext4/inode.c | 755 ++++++++++++++++++++++++++++++------
> >> fs/ext4/move_extent.c | 7 +
> >> fs/ext4/page-io.c | 105 +++++
> >> fs/ext4/super.c | 185 ++++-----
> >> include/trace/events/ext4.h | 57 +--
> >> 12 files changed, 1153 insertions(+), 589 deletions(-)
> >>
> >> --
> >> 2.46.1
> >>
> >>
>